Looking for Brinkley/Nichols in AR

I've been researching my great grandparents and I've more or less come to a dead end. My great grandmothers name was Ruby [Brinkley] Nichols, Born Jul 23 1906, Died Sep 20 1989. I've found pictures of her headstone to prove this. Her fathers name was William Brinkley, Born 1879, Died 1958, Married to Eulie M. [Bowens?] Brinkley. His mother was Nancy Eliza Brinkley, born 1858, died 1954. William, Eulie and Nancy were all buried together, of which I have a picture of the headstone to prove the above mentioned dates. I have no more information and cannot find them listed in any census in AR. All of the above mentioned have been from Poinsett, AR.